Poly(ethylene-2,6-naphthalene dicarboxylate), referred to as PEN, has been used in films, fibers, and molded objects. U.S. Pat. Nos. 3,546,008, 3,563,942, 3,734,874, 3,779,993 and 3,828,010 disclose water-dispersible copolyester and polyesteramide compositions containing metal sulfonate groups. The Tg of the polyesters is 29.degree.-55.degree. C. U.S. Pat. No. 4,480,085, discloses compositions containing at least 35 mole % of an ortho-phthalic acid, based on total dicarboxylic acid content. In U.S. Pat. No. 4,480,085, 1,8-naphthalene dicarboxylic acid and sodiosulfoisophthalic acid were used as the dicarboxylic acid component in combination with ethylene glycol and the polyester had a Tg of 73.degree. C. It is well known in the art, however, that increasing the glass transition temperature of such polyesters reduces the water-dispersibility of the polyesters.
In contrast, the present inventors have unexpectedly determined that water-dispersible sulfo-polyesters having a glass transition temperature of greater than 89.degree. C. can be prepared. The sulfo-polyesters of the present invention have a dicarboxylic acid component of poly(ethylene-2,6-naphthalene dicarboxylate and a sulfo-monomer, and a diol component of at least 35 mole percent of a diol selected from ethylene glycol, diethylene glycol, 1,4-cyclohexanedimethanol, propane-1,2-diol and 2,2-dimethyl-1,3-propanediol.